Human apoB isoforms have been analyzed in human intestinal organ cultures in adults and children. The secreted apoB isoproteins were analy by NaDodS04 gel electrophoresis and immunoblot analysis utilizing apoB monoclonal antibodies. The results of these studies established that the human intestine secretes both apoB-48 and apoB-100, with apoB-100 being the predominant apoB isoprotein secreted by the intestinal organ cultures in vitro. These results are of major importance since apoB-100 containing lipoproteins are known to be atherogenic. Apolipoprotein variants have been isolated from patients with dyslipoproteinemias. ApoA-IBaltimore (arg more than leu) has been isolated from a kindred with familial hypoalphaalipoproteinemia and premature cardiovascular disease. Purified apolipoprotein has been utilized in kinetic studies which established that the amino acid substitution was not associated with any change in the metabolism of apoA-I. ApoE-1Harrisburg has been purified from a kindred with a dominant form of type III hyperlipidemia. The sequence of apoE- 1Harrisburg was determined and shown to be a glutamic acid for lysine substitution at position 145. The metabolism of apoE- 1Harrisburg was analyzed, and the catabolism of the apoE variant was markedly delay when injected into normal volunteers.